Method of coating articles with a film-forming material

ABSTRACT

THE SPRESENT INVENTTION CONCERNS A PROCESS FOR COATING A SURFACE WITH A FILM-FORMING MATERIAL DISSOLVED OR DISPERSED IN A CHLORINATED SOLVENT, WHICH COMPRISES (1) RAISING THE TEMPERATURE OF THE SURFACE WHILE THE SURFACE PASSES THROUGH A FIRST ZONE CONTAINING THE SATURATED VAPORS OF SAID SOLVENT, APPLYING SAID FILM FORMING-MATERIAL IN A SECOND ZONE AND REMOVING THE SOLVENT FROM SAID FILM BY MAINTAINING SAID SURFACE HAVING SAID FILM IN SAID SECOND ZONE IN IMMEDIATE CONTACT WITH AIR OR OTHER INERT GAS HAVING A SOLVENT RELATIVE HUMIDITY PREFERABLY LESS THAN 50%, AND DURING WHICH PERIOD THE SURFACE TEMPERATURE   IS RAISED ABOVE THE BOILING OF THE SOLVENT, INTRODUCING THE SURFACE INTO A THIRD ZONE CONTAINING SATURATED VAPORS OF SAID SOLVENT AND FINALLY WITHDRAWING THE SURFACE COATED WITH THE FILM TO THE AMBIENT ATMOSPHERE, WITHDRAWING THE SOLVENT LADEN AIR FROM SAID SECOND ZONE, REMOVING THE SOLVENT THEREFROM AND RETURNING SAID AIR TO SAID SECOND ZONE.

Aug. 3, 1971 J N JR 3,597,257

METHOD OF COATING ARTICLES WITH A FILM-FORMING MATERIAL Filed July 2,1968 Dre/r2 INVENTOR. James L. Dunn, Jr:

QTTOlQ/VEV United States Patent 3,597,257 METHOD OF COATiNG ARTICLESWITH A FILM-FORMING MATERIAL James L. Dunn, Jr., Lake Jackson, Tex.,assignor to The Dow Chemical Company, Midland, Mich. Filed July 2, 1968,Ser. No. 741,939 Int. Cl. B44d 1/48 US. Cl. 117-47 1 Claim ABSTRACT OFTHE DISCLOSURE The spresent invention concerns a process for coating asurface with a film-forming material dissolved or dispersed in achlorinated solvent, which comprises (1) raising the temperature of thesurface while the surface passes through a first zone containing thesaturated vapors of said solvent, applying said film forming-material ina second zone and removing the solvent from said film by maintainingsaid surface having said film in said second zone in immediate contactwith air or other inert gas having a solvent relative humiditypreferably less than 50%, and during which period the surfacetemperature is raised above the boiling point of the solvent,introducing the surface into a third zone containing saturated vapors ofsaid solvent and finally withdrawing the surface coated with the film tothe ambient atmosphere, withdrawing the solvent laden air from saidsecond zone, removing the solvent therefrom and returning said air tosaid second zone.

DESCRIPTION OF INVENTION In accordance with the present invention asurface, such as metal, plastic, wood or fabric, upon which it isdesired to deposit a coating is introduced into a first zone wherein thesurface is heated to the boiling point of the solvent to be employed inthe coating composition. This first zone is filled with saturated vaporsof the solvent in which the film-forming material or coating isdissolved or dispersed. During passage through said zone the surfaceabsorbs sensible heat sufficient to raise its temperature to about thetemperature of the vapor atmosphere. The surface then is introduced intoa second zone wherein two operations are carried out. Firstly, thefilm-forming or coating composition is applied to the surface. Thisoperation can be conducted by spraying the surface or dipping thesurface into a bath of said film forming composition or coating orapplying the filmforming composition by the technique of electrostaticcoating. The surface is then subjected to intimate contact with an inertgas, such as air or nitrogen, argon, helium or the like, which has asolvent relative humidity of less than saturated with the vapors andpreferably less than 50%. This gas may be cooler than the surface, thesame temperature as the surface or hotter than the surface. The gas,introduced into the second zone in a state of low solvent relativehumidity, contacts the surface, takes up solvent vapors and is removedfrom the zone to a condenser wherein the solvent vapors are condensed,at least in part, and the gas returned to the zone in a state of lowsolvent relative humidity. It is to be understood that the gas is heatedprior to re-introduction into the zone. The surface is heated to atemperature above the boiling point of the solvent either by absorptionof heat from the gas or by inductive, infrared or resistance heating.After the surface is dry, the solvent removed, the surface is introducedinto a third zone before exiting to the ambient atmosphere. This thirdzone is filled with the saturated vapors of the solvent. The surface isthen removed to the ambient atmosphere, dry.

3,597,257 Patented Aug. 3, 1971 "ice One embodiment of an apparatus asillustrated in the drawing, suitable for carrying out the presentinvention, comprises a box-like structure 10 having an opening at eachend. These openings provide an entrance 11 and an exit 12 to and fromthe interior 10A of the box-like structure 10. Surrounding each of theinterior walls 13 and 14 of the entrance 11 and the interior of walls 15and 16 of the exit 12 are a series of coils 17 and 18 and 19 and 20,respectively. Directly beneath each coil 17, 1'8, 19, and 20 are troughs21, 22, 23 and 24 respectively. Wall 1 4 and wall 16 each form a barrierextending below the opening 11 and 12 respectively, thus providing atortuous path of ingress and egress from the opening 11 into theinterior 10A of the structure 10 and from the interior 10A of thestructure 10 to the exit 11. Situated within the interior 10A at eachend 11 and 12 respectively, of the box 10 and spaced apart from thewalls 14 and 16 are a pair of walls 27 and 28. These walls 27 and 28extend from the bottom 10B of the interior 10A of structure 10 above theopening 25 and 26 to a point near the top 10C and at least as high asthe coils 17 and 18. Also located interior of each wall 27 and 28 aredownwardly extending walls 29 and 30. These walls 29 and 30 extend intointerior 10A to a point below the upper extent of walls 27 and 28.Positioned near the top 10C of box 10 in interior 10A in a distributionduct 31 which is connected to an exterior condenser 32, which may be inthe nature of a tube and shell exchanger. The exchanger or condenser 32is provided with solvent vapors by means of blower 33 Whose intake 34 islocated within the zone 10A or in this case through top 10C thusconnecting the blower 33 and exchanger 32 in fluid communication withthe interior 10A of box 10'. A heater 32A be tween the exchanger 32 anddistributor 34 provides the heat necessary to bring the gas to thedesired temperature to establish the desired solvent relative humidity.A Work carrier, not shown, but whose path 35 is illustrated in dashedlines courses the interior of box 10 in a serpentine manner, conductinga part along a path from entrance 11 through passages 25 and 36 intointerior 10A and out through passages 37 and 26 and exit 12. A sprayzone 38 is shown along the path 35 with attendant spray nozzles 39connected by piping, not shown, to a source of film-forming or coatingmaterial dissolved or dispersed in a volatile organic solvent. Boilingsumps 40 and 41 are located in the bottom of the entrance 11 and exit12, respectively, are filled with liquid to cover heating coils 42 and43. These sumps provide the source of saturated vapors to fill theentrance and exit zones to the vapor level control coils 17, 18, 19 and20. A drain 46 is provided to remove any condensate or dripping from thespray nozzles and which collect in the bottom of the intermediate zone.

The apparatus described above and illustrated in the drawing isinsulated about its exterior walls to reduce heat losses andcondensation of vapors within the chamber on the walls of the chamber.Further it is conventional to employ a cold wall on the exterior ofwalls 13 and 16 as shown at 44 and 45.

Although a spray zone has been illustrated as the means for applying thecoating or film-forming material to the parts passing through theapparatus, it is to be understood that other means can be employed withequal success. For example, the parts may be dipped into a tank or traylocated along the path 35 which contains the coating or film-formingformulation. Further, the technique known as electrostatic spraying maybe employed to coat the parts.

It is to be further understood that various means can be employed togenerate the vapors both in the entrance and exit as well as in theintermediate zone. For example,

in place of the boiling sumps 40 and 41 an external boiler may beemployed to generate the vapors and the vapors directed throughappropriate tubing or piping to each zone. A-lso liquid solvent may beheated to its boiling point or higher under pressure and delivered hotto each zone whereat upon release of pressure the solvent will vaporize.

Modifications can be made in the apparatus at entrance and exit such asplacing doors within the wells 44 and 45 which reduces solventvaporization during operation.

A preferred method for coating a surface with a filmforming materialapplied from a solution or dispersion in a solvent, such as ahalogenated solvent, comprises introducing said surface into a firstzone of vapors of the halogenated solvent, then into a second zonewherein the film-forming material is applied to said surface,maintaining said surface after application of the film-forming materialin said zone while subjecting said surface to air having a solventrelative humidity less than about 50%, removing the surface when dryinto a third zone containing solvent vapors, and continuouslycirculating the solvent laden air of said second zone through acondenser for said solvent and returning said air to said second zone,and withdrawing said surface from said third zone.

Solvents which can be employed in preparing the coating compositions andwhich can be removed in accordance with this invention are thehydrocarbon solvents such as toluene and naphtha, the halogenatedhydrocarbon solvents, such as methylene chloride, dichloroethane,1,1,1-trichloroethane, perchloroethylene, trichlo roethylene,fiuorinated hydrocarbons and the like.

I claim:

1. A method for coating a metal, plastic, wood or fabric with afilm-forming material dissolved or dispersed in a volatilizable organicsolvent which comprises; raising the temperature of the surface Whilethe surface passes through a first zone containing the saturated vaporsof said solvent, applying said film-forming material in a second zoneand removing the solvent from said film by maintaining said surfacehaving said film in said second zone in immediate contact with air orother inert gas having a solvent relative humidity preferably less thanand during which period the surface temperature is raised above theboiling point of the solvent, introducing the surface into a third zonecontaining saturated vapors of said solvent and finally withdrawing thesurface coated with the film to the ambient atmosphere, withdrawing thesolvent laden air from said air in said second zone, condensing at leasta part of the solvent therein heating said air to a temperature toprovide the desired solvent relative humidity, and returning said air tosaid second zone.

References Cited UNITED STATES PATENTS 2,763,575 9/1956 Bede 1l7lO5.3X2,861,897 11/1958 Hendrixson 1l7l05.3X 3,042,547 7/1962 Pickett ll7--l023,073,721 1/1963 Pockorny ll7-47X WILLIAM D. MARTIN, Primary Examiner W.R. TRENOR, Assistant Examiner U.S. Cl. X.R.

